Add support for iPXE over IPv6 in the ML2/OVN DHCP implementation

[Slawek Kaplonski]

Core OVN recently added (v. 23.06.0) support for BM provisioning over IPv6 - see commit https://github.com/ovn-org/ovn/commit/c5fd51bd154147a567097eaf61fbebc0b5b39e28
We should add support for it in Neutron ML2/OVN backend.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/neutron/+/890683

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/neutron/+/890683
Committed: https://opendev.org/openstack/neutron/commit/034fcb0f6d9fa3851ce960fd130ea33dc78e2b06
Submitter: "Zuul (22348)"
Branch: master

commit 034fcb0f6d9fa3851ce960fd130ea33dc78e2b06
Author: Slawek Kaplonski <email address hidden>
Date: Mon Aug 7 17:02:26 2023 +0200

    [OVN] Add baremetal support without Neutron DHCP agent for IPv6

    Support for the required DHCPv6 options was recently added in core
    OVN with [1].
    This patch adds support for that in ML2/OVN backend also and by that
    closing one of the gaps between ML2/OVN and ML2/OVS backends.

    This patch also adds upgrade check to check used ovn version and warn
    operators if native OVN DHCP is used for BM provisioning and OVN version
    is older than 23.06.0.
    Unfortunately there is no easy way to check used version of OVN so check
    relies on the ovnnb schema version.

    [1] https://github.com/ovn-org/ovn/commit/c5fd51bd154147a567097eaf61fbebc0b5b39e28

    Closes-Bug: #2030520
    Change-Id: Iaa3ff8e97021e44f352e5a9a370714bf5f1d77b8

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/neutron 24.0.0.0b1 development milestone.